红条毛肤石鳖齿舌主侧齿中铁还原酶分布及与生物矿化的关系

以红条毛肤石鳖Acanthochiton rubrolineatus(Lischke)齿舌为材料,通过切片和酶组织化学技术,在光镜和电镜下对齿舌主侧齿的微结构及高铁还原酶的存在进行观察,从微观角度了解齿舌主侧齿齿尖的矿化机理。结果显示,成熟主侧齿由齿尖和齿基组成。齿尖结构由外至内分为三层,最外层为磁铁矿层,前后齿面磁铁矿层的厚度不等,后齿面约50μm,前齿面约5—10μm。向内依次为棕红色的纤铁矿层,厚约10μm,及略显黄色的有机基质层,有机基质层占据着齿尖内部的大部分结构。高分辨透射电镜下显示磁铁矿由条状四氧化三铁颗粒组成,长约2—3μm,宽约100—150nm。齿舌的矿化是一个连续过程,不同部段处于不同的矿化阶段,齿舌囊上皮细胞沿囊腔分布,并形成齿片。未矿化的新生主侧齿齿尖中存在由有机基质构成的网状结构。随矿化的进行,有机基质内出现矿物颗粒。初始矿化的齿尖外表面有一个细胞微突层,微突的另一端为囊上皮细胞,矿物质经由微突层达齿尖并沉积于有机基质中,齿尖随之矿化并成熟。初始矿化齿尖的外围有大量的三价铁化物颗粒,稍成熟的齿尖外围同时还出现二价铁化物。新生或初始矿化主侧齿齿尖外围的囊上皮细胞中有大量球形类似于铁蛋白聚集体的内容物,直径0.6—0.8μm,球体由膜包围。齿舌囊上皮组织中存在三价高铁还原酶,此酶分布于上皮细胞的膜表面,可能与齿尖表面磁铁矿的生成有一定的关系。

THE DISTRIBUTION OF THE FERRIC REDUCTASE AND BIOMINERALIZATION OF THE MAJOR LATERAL TOOTH OF THE CHITON ACANTHOCHITON RUBROLINEATUS

The radula in the chitons is a ribbon-like apparatus which bears a series of distinctive mineralized teeth called the major lateral teeth. Great amounts of minerals including magnetite have been deposited at the cusps of the teeth. The magnetite mineralization could harden the teeth. In order to investigate the mechanism of the biomineralization of the cusp, the radulae of chiton Acanthochiton rubrolieatus Lischke were extracted and posterior ends of the radulae approximately 0.5 cm in length were fixed, sectioned and observed with light microscope, scanning electron microscope and transmission electron microscope. In addition, aimed to display the iron minerals, the existence and the distribution of the ferric reductase, the sections were examined by histochemistry technology. Results showed that the radula underwent a mineralization progress and the different parts of the radula exhibited various mineralization degrees; the major lateral tooth cusp was a composite structure made up of three distinct layers from the outer to inner. The black magnetite layer was about 50 ?m in thickness on the posterior edge, and 5—10 ?m on the anterior edge. The lepidocrocite layer in red-brown color below the magnetite layer was only 10 ?m in thickness; the core was the yellow organic fibril layer. Magnetite particles which constituted the magnetite layer presented chip-shaped pieces and were 100—150 nm in width, hundreds of nanometers to several micrometers in length; moreover, all the magnetite particles were arranged to be parallel to the length axis of the tooth cusp. Radular teeth including the major lateral teeth were formed by epithelial cells of the radular sac, and the epithelium lining the lumen of the radular sac varied markedly along its length. Newly formed major lateral tooth cusp was almost composed of organic matrix, and the fibrous matrix presented meshwork-like appearance. With the development of mineralization, some fine mineral granules began to be deposit into the organic matrix of mineralizing major lateral tooth. The minerals first appeared in the organic matrix were ferric iron minerals, then ferroc iron minerals. Along the outer surface of mineralizing major lateral tooth cusp surrounded by epithelium of the radular sac, a microvilli-like structure was formed, by which minerals gradually were transported into the cusp. Iron-containing minerals presumably originated from the inclusions which were membrane-bound aggregates of resembling ferritin molecules with 0.6—0.8 ?m diameter in surrounding epithelium of the radular sac. The ferric reductase occurred in the epithelial tissue of the radular sac, and mainly distributed on the membrane of these epithelial cells, furthermore, it may be involved in the formation of the magnetite mineralized in the cusp.